The aim of all height-adjustable chairs is to make a working area easy to reach. A working area of this type may, for example, be a table or desk, a moving belt or a production station, a patient's chair or an operating table.
Numerous designs of work chairs of this type are known. Individual differences in body length have led to height-adjustable work chairs with various forms of seats which are likewise semi-adjustable and/or tiltable. Hitherto, however, no work chair has been disclosed which actually takes full account of the individual size of a person. Most chairs are either too small for tall users or too large for small users.
In addition, sitting in a raised position on a traditional seat—depending on the dimensions of this seat—leads to undesirable pressure effects on both the vascular system and the muscular system.
Nature designed the human leg and pelvis complex for people to be standing and walking in an upright position. Therefore, it is explained in anatomical manuals that the muscle masses are located on the opposite side from the direction of movement. Therefore, the lower leg being at the front, the muscle mass is on the rear side, the upper leg being to the rear, the muscle mass is at the front, and the pelvis being at the front, the muscle mass is at the rear side. The upper and lower legs pivot with respect to one another at the knee, the upper legs and pelvis do the same at the hip joints. These anatomical facts mean that at the back of the knee there is a sharply delimited transition from the upper leg to the lower leg, whereas the transition from the pelvis to the upper leg has a relatively rounded boundary in the form of the horizontal buttock pleat. This pleat is partially dependent on the mass of the buttock and thigh muscles. In anatomical terms, the sitting posture is characterized by support on the ischium nodes of the two halves of the pelvis. In mechanical terms, for a balanced sitting posture, it is most expedient for the thigh bone position to be horizontal and the position of the lower leg to be vertical.
The anatomical-mechanical data are independent on the notion comfort. The latter is partly determined by the extent of support for the upper legs, the extent to which the seat is tilted backwards and the degree of support for the back.
However, this information is not relevant or is differently relevant when designing a work chair. Here, the starting point needs to be the possibility of adopting an active working posture, upright and symmetrical, i.e. for the head/neck posture, shoulder position and the forwards movement of the upper arm and upwards movement of the lower arm/hand with respect to the horizontal position not leading to injury to or overloading of the kinetic chain of the human body.